The present invention relates generally to a control system, and in particular to a system and method for sensor validation and fusion of signals from a plurality of sensors in a control system.
A sensor or detector is a device that is operable to respond to a physical stimulus, such as heat, light, sound, pressure, magnetism, an electric field, or a particular motion, and to transmit a signal representative of the physical stimulus in response to the physical stimulus. The signal may be used for measurement purposes and/or for control of a system. Some types of sensors are direct indicating, e.g., a mercury thermometer. Other types of sensors may be paired with an indicator, so that the signal representative of the physical stimulus is in a form that is understandable.
Typically, a control system uses a signal from a single sensor to control the operation of a device or system. For example, an air conditioner may use a thermostat to control the operation of the air conditioner. The thermostat may be set for a desired temperature. The thermostat also has a sensor to sense the actual temperature. When the actual temperature is above the desired temperature, the thermostat directs the air conditioner to provide cooling to reduce the actual temperature below the desired temperature. Conversely, when the actual temperature is below the desired temperature, the thermostat directs the air conditioner to cease cooling.
However, other control systems use signals from a plurality of sensors to control the operation of a device or system. Various schemes may be utilized to control the operation of a system that receives signals from a plurality of sensors. For example, the system may be configured to control the system based on the single sensor that represents the greatest value of the control parameter. In the example provided above, an air conditioner could be provided with input from several temperature sensors and use the temperature sensor that provided the signal corresponding to the hottest temperature to control the operation of the air conditioner. Alternatively, the control system could establish an average value and use the average value to control the system.
Furthermore, there are a number of problems associated with each of these methods of control. For example, these control schemes may not control the system correctly when a sensor fails. Some sensors can fail high, i.e., the sensor provides a signal that represents a greater parameter value than the actual parameter value when the sensor fails. In this scenario, a control scheme that uses the greatest signal produced by the sensors could utilize a signal from the failed sensor to control the system as a result. In addition, a system that averaged the signals would also control the system based on an average value that was higher than the actual value. Similarly, a sensor can fail low, i.e., the sensor produces a signal that represents a lower parameter value than the actual parameter value, or no signal at all, when the sensor fails. A sensor that failed low would produce a lower average value for control. In addition, the signals from the sensors can drift over time or experience noise. All of these conditions may also result in the control system using erroneous parameter values to control the operation of the system. As a result, the control system may initiate control functions based on a faulty signal from the sensors.
Accordingly, an improved technique is desired that enables a plurality of sensors to be used to control the operation of a system without the drawbacks of the schemes described above. More specifically, a technique is desired to enable a system that controls the operation of a system based on signals from a plurality of sensors to operate when a sensor fails or when the signal from a sensor begins drifting away in value from the signals provided by the other sensors.